The demand for ballast used in railway track laying and road construction has increased sharply in recent years. One reason for this is certainly the general increase in population mobility and freight traffic. Rail traffic, in particular, comprises an ever-increasing proportion of high-speed trains with a large axle load. The enormous displacement forces they cause are transmitted via the rails to the sleepers and from there to the ballast. The stone formation changes over time and individual ballast stones become distorted, shifted and rounded, so the position of the tracks is changed and cost-intensive and time-consuming repair work has to be carried out at regular intervals.
Various methods of consolidating ballast with the incorporation of plastics have already been described in the past (DD-A 86201, DE-A 3941142, DE-A 19711437, DE-A 19651755, DE-A 3821963, DE-A 19811838).
DE-A2063727 describes a method of reducing lateral track buckling due to lateral displacement forces. In this case the binder is sprayed onto the ballast bed in the form of a high-viscosity plastic and the ballast stones are adhesively bonded together at the points of contact. A possible alternative is 2-dimensional adhesive bonding of the ballast stones by injection of the binder in the form of a 2-component synthetic resin.
DE-A 2305536 describes a method of raising railway sleepers and road surfaces by the introduction of a swelling agent, which then solidifies. The swelling agent is e.g. a multicomponent plastic such as polyurethane foam. The liquid plastic is applied through a hole in the sleeper using a filling probe.
JP-A 8157552 describes the preparation of polyurethane resins which cure in the presence of moisture and are used to stabilize piles of stones. The polyurethane resins are prepared using aromatic polyisocyanates, monofunctional poly-ethers and amino-initiated polyethers and applied by means of spraying processes.
EP-A 1979542 describes a method of consolidating ballast, wherein ballast stones are spread out to form ballast and reaction mixtures of isocyanate components and polyol components for the preparation of polyurethane foams are applied between the spread ballast stones.
EP-A 2150652 describes a process for the partial or complete foaming in situ in the scaffold of a ballast bed, wherein the reactive components are fed into a high-pressure mixing head, where they are mixed, and the free-flowing reactive mixture discharged from the high-pressure mixing head is applied to the surface of the ballast scaffold.
A common feature of the methods described above is that they produce ballast which can only be stabilized unselectively with the aid of plastics. Furthermore, in some cases the methods described rely on a relatively complicated application technique, or the operation is carried out under high pressure in order to mix the reaction components thoroughly. In particular, there is no possibility of a flexible variation in the proportion of catalyst or activator in order to adapt to a change in ballast depth, porosity or temperature. In this application it is typical to use chemical systems which have extremely different proportions of the components in the mixture, e.g. 1 part catalyst: 100 parts polyol component. In the high-pressure technique these cannot be adjusted to other proportions with sufficient speed and accuracy. Alternatively, it would be necessary to have high-pressure mixing heads of much more complex design and to accommodate additional storage containers in the already restricted space on the track wagon from which the application is made.